Scanning force microscope (SFM) was operated in the lateral-force mode with different loading forces. The mica samples were irradiated by Se ions with a kinetic energy of 11.4 MeV/u. The "full-height width" and the "half-height width" of track profiles were used to evaluate the ion-track diameter. For the former method, the average track diameter increases slowly with increasing loading force between SFM tip and sample. For the later method, the average diameters of ion track nearly keep a common value as the SFM loading force increases.